Glycosylated proteins are present in the extracellular matrices and cellular surfaces of many cells. Glycoproteins are organic compounds composed of both a protein and a carbohydrate joined together by a covalent linkage. The oligosaccharide moieties of the glycoprotein are implicated in a wide range of cell-cell and cell-matrix recognition events.
The addition of the carbohydrates on the protein involves a complex series of reactions that are catalyzed by membrane-bound glycotransferases and glycosidases. The types and amounts of sugars that are attached to a given protein depend on the cell type in which the glycoprotein is expressed. In addition, the types of linkage used to join various sugar groups together also confound the complexity of glycosylation.
The biological activities of many glycoproteins are not detectably different if the carbohydrates are removed. However, glycosylation of proteins may have several effects. Carbohydrates often lengthen the biological life of a protein by decreasing the protein's rate of clearance from the blood. In addition, the carbohydrates may help the protein to fold properly, stabilize the protein, or affect physical properties such as solubility or viscosity.
It is estimated that 40% of the United States population are consuming nutritional supplements (for example, vitamins and minerals) (Meyers D G, et al. 1996. Arch Intern Med. 156:925). These supplements are ingested to compensate for inadequacies in ones diet and for the health benefits they provide. In addition, in certain situations in the medical, home health care, and nursing home facilities, patients are given either an enteral or parenteral feeding mixture which contain vitamins and minerals.
The absorption of various vitamins and minerals are affected by numerous factors, including diet. For example, high intakes of iron, zinc, or manganese can interfere with cooper absorption (Johnson M A, et al. 1998: Am. J. Clin. Nutr. 67:1035S). Furthermore, the absorption of iron from the diet is extremely poor. Several dietary factors can enhance the absorption of iron, including vitamin C (Zijp I M, et al., 2000. Crit. Rev. Food Sci. Nutr. 40:371) and vitamin A (Layrisse M, et al. 2000. Arch Latinoam. Nutr. 50:243).
However, the stability of various vitamins (including vitamin C and vitamin A) and mineral are degraded by several environmental factors. For example, vitamin C is degraded by oxygen present in the atmosphere (Nagy S. et al. 1977. J. Argic. Food Chem. 25:135). Moreover, vitamin A is degraded by photolysis while vitamin E is degraded by photo-oxidation (Allwood M C et al. 2000. Clin. Nutr. 19:339).
Analysis of parenteral nutrition mixtures during infusion in daytime administration demonstrated that vitamin A loss occurs rapidly during infusion, resulting in up to 80% loss in 6 hours. This loss in vitamin A was also observed with protection of the vitamin from light (Allwood M C et al. 2000. Clin. Nutr. 19:339).
Another study examined vitamin A levels of enteral feeding formulas stored in the dark. These feeding bags provide a vitamin A level that is 1.6 times above that of the U.S. daily recommendation. After 9 months of storage, the vitamin A level dramatically dropped to 0.2 to 0-fold of the U.S. daily recommendation (Frias J. et al. 2001. J. Agric. Food Chem. 49:2313).
Therefore, there is a need for compositions containing biologically active ingredients with an improved bioactivity and stability and methods of making such compositions.